Yes, exactly that, modulation depth. The screen goes completely dark, and our brains don't like it because: 1. It's stressful that something disappears abruptly

Yes, exactly that, modulation depth. The screen goes completely dark, and our brains don't like it because: 1. It's stressful that something disappears abruptly. 2. It's stressful that it later appears a bit shifted in space.